Adiposity (or excess fat in the subcutaneous cellular tissue) can have many causes that are more or less complex.
Some skin cells, called adipocytes, contain variable amounts of fats in the form of triglycerides, these triglycerides being synthesized in vivo by the adipocytes themselves, according to enzymatic-type reactions (lipogenesis), from the free fatty acids and the glucose (after degradation of the latter to glycerol) contained in the body and introduced therein through certain foods. Now, in parallel, the triglycerides thus formed, and then stored, in the adipocyte cells can also redecompose, still under the action of specific enzymes (lipolysis) contained in these same cells, this time releasing, firstly, fatty acids and, secondly, glycerol and/or monoesters and/or diesters of glycerol. The fatty acids thus released can then either diffuse in the body in order to be consumed therein or converted in different ways, or can be taken up again (immediately or a little later) by the adipocytes in order to again generate triglycerides by lipogenesis.
If, for various reasons (overly rich food, inactivity, ageing and the like), a substantial imbalance becomes established in the body between lipogenesis and lipolysis, i.e., more precisely, if the amounts of fats formed by lipogenesis become appreciably and constantly greater than those which are eliminated by lipolysis, an accumulation of triglycerides then takes place in the adipocytes, which, if it becomes excessive, may be reflected gradually by the appearance of thick skin, the surface of which is often non-uniform (“orange-peel skin”) and of more or less flaccid or gelatinous consistency, finally giving the figure a general ungraceful appearance which may evolve from a simple local excess (lipodysmorphia) and the formation of cellulite, passing through a certain level of stoutness and ending at real obesity.
Now, given in particular the deep discomfort, both physical and aesthetic and sometimes psychological, that adiposity and cellulite cause among individuals who are affected by them, in particular among women, they nowadays constitute a condition that is increasingly less well tolerated or accepted.
Solutions have therefore been proposed, in the prior art, for intervening on fatty acid metabolism, which is, as has been seen, one of the favoured targets in the control of this excess of fats in adipocytes.
This can be modulated:    either by blocking glucose transport inside the adipocyte, which results, as has been seen, in a decrease in fatty acids entering the adipocyte,    or by inhibition of lipoprotein lipase,    or by activation of triglyceride lipase (or hormone-sensitive lipase), generally by stimulating cyclic AMP, for example by activation of adenyl cyclase, or by causing accumulation thereof by inhibition of phosphodiesterase.
Other biological approaches have been explored for acting on the mechanism of lipogenesis and/or of lipolysis. It has thus been proposed to use neuropeptide Y (NPY) receptor antagonists, neuropeptide Y being a neuromediator involved in a certain number of physiological processes and the involvement of which in the regulation of lipolysis it has been possible to demonstrate (P. Valet, J. Clin. Invest., 1990, 85, 291-295). It is also possible to use αz receptor antagonists or alternatively β3-adrenergic receptor agonists.
The cosmetic compositions proposed to date for the purpose of treating adiposity therefore contain “slimming” compounds which act on one or more of the mechanisms mentioned above. Among these, mention may more particularly be made of xanthine bases (i.e. xanthine derivatives), such as theophylline, caffeine, theobromine.
However, xanthine bases such as caffeine have the drawback of conferring on the slimming compositions poor cosmetic properties that are experienced by the user after application of the composition to the skin. The treated skin exhibits a tacky effect, feels taut and lacks softness: these harmful properties are not satisfactory to the user.